Known in the art are dry film photoresists comprising flexible laminar systems incorporating a solid polymeric base (substrate)-usually polyethyleneterephthalate with a thickness of 20-25.mu., an adhesive (especially upon heating) light-sensitive layer with a thickness of essentially 18-100.mu. and a protective polymeric film (generally polyethylene film) preventing the light-sensitive layer from dust and sticking when reeled (cf. British Pat. No. 1,361,298 Cl. C3G2, published July 1974; U.S. Pat. No. 3,873,319 Cl. 96-87R, published Mar. 25, 1975).
One of the prior dry film photoresists comprises a flexible laminary system incorporating a solid polyethyleneterephthalate substrate with a thickness of from 5 to 100.mu., a light-sensitive layer with a thickness of from 5 to 1,000.mu. containing a light-sensitive compound capable of forming free radicals upon exposure to UV-light-ethyl ether of benzoin, a saturated compound containing in its molecule ethylene-type ##STR1## and a product of addition of methacrylic acid to epoxy resin based on 4,4'-dihydroxy-2,2-diphenylpropane and a polymer which is a film-forming component of the light-sensitive layer-a copolymer of styrene with monoisobutyl ether of fumaric acid (50:50 mol.%), and a protective polymer film with a thickness of from 5 to 100.mu. being over the light-sensitive layer so that the adhesion of the protective film to the light-sensitive layer is smaller than the adhesion of the solid polymer substrate (polyethyleneterephthalate film) to the light-sensitive layer; adhesion values of the layers are inferior to the cohesion values of these layers thus providing the possibility of a successive stripping-off first of the protective film and then the solid polymer substrate from the light-sensitive layer.
The light-sensitive layer may also incorporate a dyestuff such as "methyl violet", a radical-polymerization inhibitor such as hydroquinone, a plastifying agent such as glycerol-1,3-dipropionate (cf. British Pat. No. 1,549,952 Cl. G 03 C 1/68 1/71//C 08 F 2/50, published Aug. 8, 1979).
Resolution of dry film photoresists depends, to a considerable extent, on the thickness of their transparent polymeric base (substrate) which separates the photographic template from the light-sensitive layer upon exposure. When a thinner base is used, the pattern of the protective relief is less distorted and the resolving power of a dry film photoresist is increased.
However, the use of a film base with a thickness of below 20.mu. in the manufacture of the prior art photoresist causes difficulties associated with casting of the lightsensitive layer and drying thereof due to a low mechanical strength of thin films and possibilities of their warping especially inside the hot section of the drying chamber of a casting machine, as well as upon the application of the photoresist onto board blanks thus causing undergrade quality of the resulting articles. Thus, upon casting of the lightsensitive layer onto a polyethyleneterephthalate film with a thickness of 10.mu. polymeric substrate warping as high as 5 mm is observed. The difference in thickness of the light-sensitive layer in this case may be as high as 30 to 50% and over. During the application of such a photoresist onto board blanks by means of a roller-type laminator folds are formed which break the integrity of the light-sensitive layer due to a strong deformation of the base. For this reason the prior at photoresists have a thicker base (20-25.mu. and above) thus ensuring a lesser warping in the manufacture and use of photoresists.
Therefore, the above-mentioned limitations substantially restrict the field of application of known dry film photoresists.